Ayatollah Ali Khamenei, Iran's supreme leader, has hardened his stance in nuclear negotiations with world powers, saying he rejects a long-term freeze on nuclear research and wants to ban international inspectors from accessing military sites.

Signaling that Tehran may be toughening its stance ahead of an end-of-June deadline for a nuclear deal with world powers, Khamenei called demands that Iran halt the research and development portion of its nuclear program "excessive coercion."

"We don't accept 10-year restriction. We have told the negotiating team how many specific years of restrictions are acceptable," Khamenei said. "Research and development must continue during the years of restrictions."

Iran's parliament has already passed a bill that, if ratified, will ban access to Iranian military sites, documents, and scientists as part of any future deal. The bill must be ratified by the Guardian Council, a constitutional watchdog, to become a law.

Meanwhile, the Associated Press news agency reported that the West is ready to offer high-tech reactors and other state-of-the-art nuclear equipment to Tehran if it agrees to restrict programs that can make atomic weapons.